We will focus on the characterization of MIs locus products (especially Ly-m20 and Ly-m22 alloantigens) in terms of their serology, immunobiological function, and biochemical structure. Ly-m20: The biochemical characterization will be concluded by Dr. Palfree. Current data point to the structure of a 60 kilodalton protein molecule. Polysaccharide moieties, polypeptide chain composition, and substructure will be determined. As we have derived five monoclonal antibodies, we will test by sequential precipitation whether all determinants reside on the same molecule. We\are interested in the gene structure and have initiated a collaboration with Dr. B. Huber at Tufts Medical School. In functional terms, the central issue is whether Ly-m20 is the product of the MIs locus itself. Hence, experiments to inhibit MIs stimulation by anti-Ly-m20 antibody will be initiated. A collaboration with Dr. Charles Janeway at Yale has been organized. Dr. Mark will complete the serological studies on the expression of Ly-m20 on hemopoietic precursor cells and stem cells. Expression of other monocytic cells will be studied by FACS analysis. This work will be done in part at SKI (normal cells) and at NIH together with Dr. Sandy Morse (tumor cell lines). Ly-m22: In view of the importance of Ly-m22 as a marker of T-suppressor cells, we will initiate a biochemical study to isolate and characterize the molecule. The functional studies will continue. In a sequel to the finding of Ly-m22 as a unique marker of nonspecific T-suppressor cells, we will establish and test systems of antigen-specific suppressor cells. Ms. Marion Chan (the graduate student instrumental in discovering the functional association of Ly-m22 with suppressor cells) will inquire into the Ly-m22 phenotype of helper and cytotoxic precursor cells. Upon completion of the serology of Ly-m22, we will study its expression on B-\and T-cell lines by fluorescence in collaboration with Tom Chused at the NIH. (LB)